I only noticed this puzzle last night. I've found hundreds of puzzles in this area so I really don't know how I managed to overlook this one for over four and a half years.
The usual method I use for picture puzzles didn't give me anything, but I had also noticed something that was triggering memories from years ago. A quick google confirmed things - and yes it looked like it would give me a way in.
With the theme confirmed it was then just a matter of identifying each of the pictures. I spent a leisurely hour doing that and enjoyed reading some of the associated wiki pages. I had seen that the previous two solvers had failed to identify one of the pictures, so stopped when I had one to go assuming that it was now missing. However on re-reading I saw that it was "H" that stoneysjl couldn't find, and I had that one.
Some puzzles of this type often have an unusual decode method, but happily the first thing I tried worked. I was grateful for the geochecker and the hint it contained.
I had arranged to pick it up today with Bobcat when he came back from the gym. We still had about three quarters of an hour until sunset when we set off, but annoyingly the roads around Owlsmoor were closed so by the time we arrived it was getting dark. We had a quick look around the obvious tree (unfortunately startling a small bird). With no obvious place to hide a cache there I moved on to the next and quickly found the cache. Nice one.
I see that it was last found May 2016 so we have resuscitated it - it's ALIVE!!!!
We decided to celebrate with a bag of chips - we made it to the chippie just as they were closing. We also saw two deer and a fox on our journey home.